Various procedures have been developed to identify volatile components and concentrations thereof in a flowing stream. Such procedures include the combining of a liquid with a gas containing the components to be identified, inducing a reaction product, and separating such product through dialysis. It also has been proposed to react the resultant product to form a colored product to permit analysis thereof by means of a colorimeter. Additional procedures involve purge and trap analysis which is relatively slow and somewhat complicated. For example, purge and trap analysis frequently requires as much as 45 minutes to one hour to complete.
Head space analysis, although not being an on-line technique, is used extensively. This form of analysis is generally accomplished by partially filling a sealed vial with the liquid sample, placing the vial in a temperature controlled environment to permit the volatile components to come to equilibrium with the air or gas in the head space of the vial, and then sampling the head space gas and injecting the sample into a gas chromatograph to identify the volatile components and determine their concentrations.
Flow-through purge vessels combined with a gas chromatograph or hydrocarbon analyzer have been used for on-line analysis of volatile chemicals in water. In this technique, slow response to excursions is a major disadvantage and arises from the fact that the vessel acts as a dilution flask requiring a resulting high humidity stream to be taken continuously to the analyzer.
Still another procedure consists of a combined armored silicone hollow fiber and gas chromatograph for the analysis of volatile chemicals in aqueous solutions. Such a system can be used for trace environmental monitoring. Among the disadvantages of this type of system is that cryotrapping is required to reach low detection limits and the silicone fiber may accumulate higher boiling chemicals which are not readily swept away into the vapor stream.
The known procedures do not readily adapt themselves to on-line determination of the identity and concentration of volatile chemical components in water such as process aqueous streams, scrubber solutions, sewer legs to treatment plants, agricultural fumigant distribution systems, or the like because of complexity and excessive cycle time. There is a distinct need for an improved method and apparatus for determination of such volatile compounds and their concentrations, such method and apparatus being particularly adapted for use in environmental services, as in the testing of waste water and/or the determination of distribution of volatile soil fumigants in irrigation water.